Published work points to an important role of surfactant protein A (SP-A) in innate host defense. SP-A modulates a number of host defense processes and exposure to ozone results in functional and structural alterations of SP-A. Two human genes, SP-A1 and SP-A2, and several genetic variants for each SP-A gene have been characterized. In vitro studies show functional, structural, or biochemical differences between the two genes and the gene-specific variants. SP-A levels are altered in a variety of lung diseases, and SP-A genetic variants are associated with risk for several pulmonary diseases. Our central hypothesis is that differences among SP-A variants account for differences in risk to lung disease in response to environmental insults. Our specific hypothesis is that the two human SP-A gene products are not functionally equivalent with regards to their host defense function, and that ozone exposure has a differential impact on this function. To investigate the specific hypothesis, we propose to study the effect of ozone, on pathogen-infected C57BL/6 and SP-A-/- mice (Aim 1) by assessing: a) survival with bacterial infection; b) ability to clear pathogens from their lungs and limit dissemination of infection; c) cytokine production, the in vivo phagocytic index of macrophages, and the in vivo oxidation status of SP-A; as well as, on the ex vivo host defense function of macrophages from wild type and SP-A-/- mice (Aim 2). To generate transgenic mouse lines on the SP-A-/- background that express equivalent levels of human SP-A1 or SP-A2 gene products (Aim 3). To study the impact of ozone on the SP-A1 and SP-A2 transgenic mouse lines by carrying out studies similar to those described for Aim 1 and by studying biochemical characteristics of the transgene products (Aim 4), and the ex vivo host defense function of macrophages from the SP-A1 and SP-A2 mouse lines (Aim 5). Through the proposed work we will generate an animal model to study human SP-A variants, and we will determine, in vivo, and in response to ozone exposure, the role of SP-A in host defense and assess functional host defense differences between the two human SP-A gene products. Knowledge gained may help explain and perhaps link the in vitro data with the human genetic association data, and provide insight in the understanding of the value of the SP-A gene duplication.